Ice-making machines: the theory of the action of the various forms of cold-producing or so-called ice machines - 1879 - PREFACE - THE theory of Ice-Making Machines has assumed a new importance, since it has been shown that they may be worked to an economical advantage in some sections, even where naiural ice is not diffi cult to be obtained. But aside from any question of com-4 petition with natural ice in temperate climates, the subjeet is of great interest - to those who find it desirable to produce and maintain a low temperature in places where the requisite quantity of ice would be too cumbersome, and where a refrigerating machine and its driving power can be easily accommodated. Such an example is afforded by the hold of a vessel sailing in a warm climate. The conditions of effective working of the three classes of machines are clearly set forth in this little treatise. ICE-M4KING MACHINES. - CHAPTER - IT has long been known that air is heated or cooled when compressed or dilated. The mechanical theory of heat defines the conditions under which this heating or cooling is effected, and shows that these effects are proportioned to the external work performed by the air, with - the restriction that in expanding the resistance overcome by the gas is always equal to the elastic force of the latter. I f t and tr represent successive temperatures of a unit weight of a permanent gas, which has been compressed or dila ted under conditions above stated in producing an amount of work either resistant or motive equal to W, we shall hare A being the reciprocal of the mechanical equivalent of heat xix and C being the specific heat of the gas at constant yolume. In a saturated vapor a part of the thermal equivalent of the external work is transformed into latent heat the other part alone becomes sensible under the form of external heat. This is expressed in the fundamental equation cl f - t p - p AW in which cl is the specific heat of the Iiq uid, X the proportion of vapor in the unit of weight of mixture of liquid and vapor, p the latent heat of the vapor and W the external work accomplished. TVe see from these equations that for the same quantity of heat transformed into work, the range of temperatures must be greater with a gas than, with saturated vapors. 1 2. Whether we employ a permanent gas or a vapor, the apparatus designed for the refrigerating effects is based upon the following series of operations Compress the gas or vapor by means of some external force, then relieve it of its heat so as to diminish its volume nest, cause this compressed gas or vapor to expand so as to produce mechanical work and thus lower its temperature. The absorption of heat at this stage by the gas, in resuming its original condition, constitutes the refrigerating effect of the apparatus. When the cooling takes place at constant pressure, the cycle of operations can be represented by the diagram Fig. 1 in which the abscissas represent volumes, and the ordinates pressures. The gaseous body taken at the pressure P, and under the volume V, is compressed to the tension P, and thevolume V,. It is then cooled under constant pressure so that the volume V, becomes V , then it is allowed to expand, the pressure P, becoming P, and the volume changing from V, toV,. Finally it is brought to the original volume V, by transferring heat to it under constant pressure. The area V, VYIfV, represents the work expended and the lineVoV, the refrigerating effect obtained. An inspection of the figure shows that a refrigerating machine is a heat engine reversed...